Module 7. Milk borne diseases


Lesson 27


27.1 Introduction

A variety of pathogens may gain access in to milk from different sources and cause different types of milk borne illness. Milk and its products may carry microbes or their ‘toxins’ to the consumers. Based on the type of illness produced these are categorized as food infection, food intoxication and food toxi-infection.

27.2 Types of Food Borne Illness

27.2.1 Food intoxication

Ingestion  of  pre-formed toxins, already  synthesized  by  microbes  in  food  brings  about  poisoning  syndrome  in  the  consumers and hence, is called food intoxication. Toxins affecting gastro intestinal tract are called as enterotoxins

Examples includes: Staphylococcal food poisoning, botulism, diarrohea caused by Escherichia coli, Cholera mycotoxicosis etc.

27.2.2  Food infection

Ingestion  of viable  pathogens  along  with food  leads  to  their  establishment  in  consumers  and hence is termed as food infection.

Examples includes: Typhoid, shigellosis, septic sore throat, scarlet fever etc.          

27.2.3  Food toxi-infection

Some  micro-organisms  can  produce  toxins ‘in  situ’  after  getting  ingested  with food and infect  intestine. Such type of illness is referred as food toxi-infection.

Examples includes: Bacillus cereus food poisoning and Clostridium perfringens gangrene

27.3  Milk Borne Infections

27.3.1  Salmonella poisoning

Salmonellosis is a disease resulting from the ingestion of salmonella along with contaminated food. This is mainly a food-borne illness and milk and milk products appear to be commonly involved. There are about 2000 closely related biotypes of salmonella that can cause food poisoning in humans. It is during the mishandling of milk that the causative microorganism may enter these foods and their subsequent growth during holding may lead to salmonellosis. Causative microorganism

·       Salmonella typhi– Typhoid

·       Salmonella paratyphi A, B, C – Paratyphoid

·       Salmonella enteritidis – Food poisoning  Sources

·       Water is one of the most important sources of salmonella, as it frequently gets contaminated through faecal matter. If polluted water is used for washing of utensils and equipment it can also lead to contamination of milk. Silage is another source of salmonella.

·       Handlers are the carriers in active cases.

·       External agents like flies also acts as a source of contamination.

·       Animals suffering from salmonellosis, under certain conditions, excrete viable micro-organisms in their milk.  Symptoms

a)    Typhoid fever: Characterized by continuous fever, inflammation of intestines, formation of intestinal ulcers, enlargement of spleen, characteristic raised spot eruptions on the abdomen and toxemia.

b)    Paratyphoid fever: Resembling typhoid fever but it is milder than typhoid. Approximately 105 – 107 micro-organisms per ml are required to cause infection.

c)    Salmonellosis: Nausea, vomiting, abdominal pain, diarrhoea, chills, headache, prostration, muscular weakness, drowsiness, moderate fever, restlessness etc.  Incubation period

7 – 14 days for typhoid and 1 – 7 days for paratyphoid  Diagnosis

Microorganism may be present in feces; urine and blood are identified by microscopic, cultural, fermentative and serological tests. Widal test is used for typhoid.  Prevention and control

·       Adequate treatment of water

·       Infected individuals, who had infection should not handle milk

·       Follow hygienic conditions during production, processing and storage

·       Educating the people about food and personal hygiene

·       Periodic examination of individuals who handle foods for public consumption

·       Pasteurization and other adequate heat treatment of milk and milk products

·       Control of flies

·       Treatment of affected individuals

27.3.2  Bacillary dysentery (Shigellosis)

This is one of the common food-borne infection and outbreaks are associated with consumption of unpasteurized milk.  Causative micro-organism

·       Shigella dysenteriae

·       Shigella sonnei

·       Shigella flexneri  Source

·       Milk contaminated with water, flies and utensils

·       Milk handlers  Symptoms

Shigellosis is an acute intestinal disease characterized by diarrhoea with blood, pus or mucous, fever, vomiting, abdominal cramps and tenesmus.  Diagnosis

Isolation of microorganism by taking rectal swabs and plating on desoxycholate citrate agar, incubation period is 1 – 4 days.  Prevention and control

·       Strict sanitary condition should be enforced in dairy workers particularly in pasteurization plants and retail outlets dispensing milk in bulk

·       Attendants looking after the patients should be prohibited from contact with milk or utensils

·       Take precautions to exclude flies

27.3.3  Streptococcal infection

Streptococcal infections like septic sore throat, scarlet fever and food poisoning are treated to the consumption of milk and its products. Humans and animals both can contaminate milk with streptococci. Although streptococcal food poisoning through milk and milk products is not well established, yet a few strains of Group D Streptococci or enterococci have produced toxic metabolites in milk and their toxigenic potentials is ascertained in animal models.  Causative microorganism

Streptococcus pyogenes – Scarlet fever, septic sore throat, tonsillitis and septicaemia

Streptococcus agalactiae – Mastitis in animals  Sources

·       Animals infected with Streptococcus agalactiae may harbor microorganisms in udder and acts as a source of pathogens

·       Personnel directly connected with the care and milking of animals in a dairy herd may act as vectors of mastitis and cause mastitis in other animals as these carry the pathogens on skin of hands etc

·       Enterococci are chiefly of fecal origin and fecal contamination of milk and milk products may introduce lot of enterococci in these products

·       Milking machines may help in the transfer of pathogens to milk and also to other animals with the help of infected teat cups

·       Human carriers of Streptococcus pyogenes contaminate milk during handling and processing

·       Human carriers disseminating pathogenic Streptococcus pyogenes may also infect animals that develop clinical or sub-clinical udder infections, and in turn pass out these microorganism in to milk

·       Milk products may get contaminated from raw milk infected with streptococci  Symptoms

a)      Septic sore throat: Characterized by high and irregular fever, sudden onset of fever, inflammation and swelling of lymph glands of throat and sometimes involving the formation of abscess around tonsils and in cervical lymph glands.

b)     Scarlet fever: It is an acute febrile disease of throat, accompanied by a scarlet rash. Invasion of other parts of body may occur by microorganisms resulting in infection of middle ear, kidney. Scarlet rash is due to elaboration of a toxin.

c)      Food poisoning: The symptoms resembles staphylococcal food poisoning, however, these are of mild type. Incubation period is 1 – 3 days.

d)     Diagnosis: For septic sore throat, throat swabs should be taken and observed for the presence of hemolytic streptococci of lancefield group A. Dick test is used to detect scarlet fever. Food poisoning can be diagnosed by the isolation of causative microorganisms their enterotoxin typing and toxigenicity.  Prevention and control

·        Adequate heat treatment of milk

·        Holding milk at lower temperature

·        Rejection of milk from the suspected quarters

·        Milk showing abnormal changes should not be pooled

·        Regular checking of the health of dairy workers

·        Faucal contamination of milk should be avoided

27.4  Milk Borne Intoxications

27.4.1 Staphylococcal poisoning

Infection of milk by some strains of Staphylococcus aureus leads to the elaboration of enterotoxins by these that cause gastro-enteritis in humans.  Toxins

Staphylococci produce different metabolic end products such as:


·       Haemolysin / Staphylolysin (α, β, γ and δ)

·       Leukocidin

·       Necrotizing factor

·       Lethal factor

·       Enterotoxin

·       Coagulase


Among different toxins, enterotoxin is responsible for major food poisoning out breaks. Staphylococcus aureus is capable of growing and producing enterotoxins in raw milk at a concentration of 106microorganisms per ml. However, not all the strains of microorganisms are capable of producing enterotoxins. The toxin production is faster in milk with low count. In poor quality milk, competition with other microorganisms and changes brought about by these e.g. acidity, depletion of nutrients inhibit toxin production  Sources

Human handlers are the main source as the microorganisms and present in nose, skin, wounds, pimples and boils. Animals affected with mastitis are the other sources.  Symptoms

Nausea, vomiting, abdominal cramps, diarrhoea, sweating, headache, prostration etc. Mortality is low, incubation period is 1 – 16 h., and symptoms last for 24 – 48 h.  Diagnosis

Biological methods, serological methods, coagulase test and thermo nuclease test.  Prevention and control

·       Adequate heating destroys staphylococci but not the enterotoxin. So, heating within few hours of production would inhibit the multiplication of staphylococci and hence, no toxin production

·       Adequate cooling immediately after producing milk also inhibits multiplication of staphylococci.

·       Post pasteurization contamination should be avoided

·       Infected handlers should not be allowed to handle milk

·       Animals having mastitis should be isolated

27.4.2  Botulism

Botulism poisoning is the severest of all the food poisonings, as it affects the nervous system and is often extremely fatal. However, milk is rarely involved in the causation of botulism as fluid milk is not a suitable medium for the growth of causative agent being an anaerobe. In sour milk Clostridium botulinum cannot survive due to low pH. But it is quite prevalent in canned products like condensed milk and processed cheese in view of the existing anaerobic conditions favorable for its growth.  Toxins

Although, the microorganism is heat resistant, it produces a variety of heat labile toxins that can be destroyed at 100˚C within few minutes. Different types of toxins A to G are produced by the microorganism and out of these at least four A, B, E and F are known to affect human. These toxins are lethal in small doses. It is estimated that 0.1 µg of toxin may cause death of person and 1 mg of purified toxin is sufficient to kill a population of million people.  Sources

Soil and water  Symptoms

Nausea, vomiting, fatigue, dizziness, headache, and dryness of skin, mouth, and throat. As it acts on Central Nervous System, it leads to paralysis of muscles, double vision and respiratory failure, resulting in to death. Incubation period is 12 – 96 h.  Diagnosis

Microscopic examination, animal inoculation and cultural identification.  Prevention and control

·       Adequate heating of product destroys toxin (1000C per 10 – 20 min.)

·       Hygienic conditions is adopted during production of milk

·       Chilling after production should be essential

·       Acidity inhibits the causative microorganism

·       Reject bulged cans and spoiled foods

27.4.3  E.coli poisoning

E. coli is known to be associated with enteritis in infants and adults as well as with traveler’s diarrhoea and food poisoning. Milk and milk products like ice cream, kulfi, dried milks, cheese etc can be contaminated with toxigenic E. coli that can produce the enterotoxins under favorable conditions. A minimum of 105 to 107 cells per gram are required to produce enterotoxins sufficient to cause food poisoning.  Toxins

E. coli can produce two types of enterotoxins named as heat labile and heat stable toxins. The labile toxin can be inactivated at 65˚C per30min.  Sources

·       Water supplies contaminated with fecal matter

·       Unhygienic practices by handlers may introduce the microorganism in to milk chain

·       Infected animal may also excrete the microorganisms.  Symptoms

Children are more susceptible. Symptoms due to heat labile toxins are almost similar to symptoms of cholera. Massive watery diarrhoea occurs due to accumulation of fluid in the intestines. In case of heat stable toxin, the symptoms include diarrhoea with or without vomit that is not bloody and without inflammatory exudates in stool. Fever may be present in children but not in adults. Incubation period is 8 – 24 h.  Prevention and control

·       Fecal contamination of water supply should be avoided

·       Handlers should follow strict hygiene practices

·       Cross contamination from infected animals should be avoided.

27.4.4  Cholera

Cholera is one of the acute diarrheal diseases caused by Vibreo cholerae. It frequently occurs in the form of massive epidemics. Unhygienic practices are mainly responsible for outbreak. Although, cholera is mainly water borne disease, the involvement of milk may also transmit the disease. The causative microorganism adheres to the epithelial lining of mucosa in the small intestines, where it produces enterotoxin that causes loss of fluid and electrolytes from the body followed by dehydration.  Source

·       Milk  infected by soiled hands of a patient

·       Use of infected water for dairy purpose

·       Adulteration of milk with contaminated water.  Symptoms

In mild cases of cholera, diarrhoea appears to be the only symptom. In severe cases, diarrhoea, vomiting, rice water stools, abdominal pain, thirst, dehydration are major symptoms. The disease runs a short course terminating in death, sometimes within 12 h after the appearance of first symptoms. Incubation period is few hours to 5 days, usually 3 days.  Diagnosis

Intra-peritoneal inoculation of Guinea pigs with pure culture results in the death of the animal within 24 h.  Prevention and control

·       Proper pasteurization of milk and its products.

·       Sanitary disposal of human excreta

·       Protection of water by boiling

·       Sanitary preparation and handling of products

·       Control or destruction of house flies

·       Public health education

·       Isolation of patients and carriers

·       Disinfection of stools and vomit and articles soiled by the patients

·       Food left by the patients should be burnt

·       Room of patient should be thoroughly cleaned and disinfected

·       Use of cholera vaccine in exposed population group

27.4.5  Fungal intoxications

The common types of fungal intoxications that result through milk are those caused by Asperigillus and other molds like Pencillium, Fusarium etc.  Aflatoxicosis

Aflatoxicosis is a common type of fungal intoxication caused by the common molds, Aspergillus flavus and Aspergillus parasiticus by virtue of their ability to produce aflatoxin. Aflatoxin can be present in milk as preformed toxin or it can be secreted in milk by the milch animal that has been fed with aflatoxin containing feed. Therefore, even with satisfactory sanitation and hygiene during production and processing of milk, the mycotoxins can be transferred to consumer. Upon ingestion, the aspergillus toxins are metabolized by milch animals and are secreted into milk in form of M1 and M2 that are also toxic to the consumers.

a)      Types of aflatoxins: Aspergillus flavus produces B1, B2, B2a. B1 is the most abundant and most toxic of the aflatoxin. G1, G2 and G2a toxins (produced by Aspergillus flavus only) are extremely heat stable, potent and exhibit very strong toxicity apart from being highly carcinogenic. The recommended upper permissible limit of aflatoxin in foods is 0.5µg/kg.

b)     Source: Aerial contamination and soil contaminated foods introduce mold spores in milk and milk products.

c)      Symptoms: Liver hyperplasia, tissue hemorrhage, anorexia, hepatitis and finally death in animals. The vital organs like spleen, pancreas and kidney may also be involved in aflatoxicosis.

d)     Prevention and control:

·       Prevent contamination of milk and milk products

·       Prevent fungal growth by storing the product under proper conditions and by use of fungi-static agents

·       Detoxification of aflatoxins by physical, chemical or biological agents. However, this is relatively impractical in dairy products.

27.5  Milk borne Toxi – Infections

27.5.1  Bacillus cereus poisoning

It occurs due to ingestion of contaminated food with Bacillus cereus or its spores and produces 3 types of toxins:

a)   Haemolysin

b)   Lecithinase

c)   Enterotoxin  Sources

·       From mastitis udder

·       Spores from animal’s teat and skin equipments

·       Soil – directly or indirectly  Symptoms

Two types

·       Diarrohea: Abdominal pain and cramps, profuse watery diarrhea, rectal tenesmus. Moderate nausea with rare vomiting.   Lecithinase releases phosphoryl choline, a toxic substance from lecithin

·       Vomiting: Acute attack of nausea and vomiting diarrhea is not common  Prevention and control

·       Proper cooling of milk

·       Maintenance of environmental hygiene and air quality

·       Hygiene during production, processing etc.

27.5.2  Clostridium perfringens poisoning

Clostridium perfringens- It causes gas gangrene. The anaerobic conditions inside canned foods are favourable for growth of C. perfringens. Five different enterotoxins - A, B, C, D and E are produced, where A and C causes food poisoning.  Sources

·       From soil and faeces – dust, fodder, milk

·       Faecal contamination of water  Symptoms

Diarrhoea, vomiting, abdominal pain; incubation period is 8-22 h. Sometimes it is fatal.  Prevention and control

·       Proper cooling of milk

·       Maintenance of environmental hygiene and air quality

·       Hygiene during production, processing etc.